shared hosting is just fine, as long as it provides the necessary PHP extensions and minimum versions outlined in the product pages:
Installing and running our software requires a server or webspace with PHP support and a MySQL database.
You need to have at least PHP in Version 5.3.2 and MySQL 5.1.17 with InnoDB support. It is recommended to always use the latest versions for better performance, stability and security reasons. The following PHP extensions are required to operate our software: mbstring, libxml, dom, zlib, pdo, pdo_mysql, json, pcre. The PHP safe-mode must be disabled and the memory_limit must be at least 128 MB.
The software uses about 20 MB disk space once installed. The disk and database usage raises with user activity, e.g. writing messages or uploading files.
We recommend that you contact your server administrator or hosting company to verify that your system fulfills the aforementioned requirements. In general our software installs and runs smoothly on all bigger hosting companies.
Regarding your requirement of 50 concurrent users: That's hard to properly answer. There are shared hosting plans that do fine with many more users and there are VPSes that grind to a halt with 10 concurrent users. In case you outgrow your shared hosting plan you can always switch hosts.